Caffeine Software
Caffeine is no more. The developers have moved on to newer and better things, but their apps shine on. Even though Caffeine shut it's doors before the release of Mac OS X v10.3, the version available now has been updated for it. You can purchase TIFFany at the Stone Design online store here. The home/downloads page is here, actual Apps (56 MB) for Mac OS X are here.

Scott Anguish and Stepwise
While not quite as busy as it was back before Mac OS X was released, it is still one of the best places for information. Some important links:Stepwise home pageCocoa Starting Point

RBrowser
These guys have been making the best FTP client for years. It is a must for anyone who uses Mac OS X, Rhapsody or NEXTSTEP/OPENSTEP. You can find their product pages here:RBrowers for Mac OS XRBrowser Lite for Mac OS X

Karelia Software
The maker of Watson, an application way ahead of it's time. Sadly (like animal that eat their young) Apple reworked Sherlock into a poor, under support knock off of Watson and bundled it with Mac OS X starting with v10.2. Apple missed the point of Watson though. Watson is a web services development platform. That is to say, Watson is the foundation for the web tools that other people could make.

Sun Microsystems bought Watson, but has yet to release the reworked version (which is supposed to work on Macs, Linux, Solaris and sadly Windows). You can download a copy of the last version here and the Karelia blog has the activation information for those who still want to use it (it is free and therefore unsupported). The Watson home page is here